Ummmm .....
Not so sure about some of this reasoning.
Whether a substance is in a liquid or gaseous stage - it still retains it's chemical nature.
Paint as a liquid - has vapors associated with it. The paint vapors are still as noxious or toxic as the liquid itself. Sometimes more so, depending upon the animal and the concentration to which it is exposed.
Airborne vapors are absorbed by the bloodstream in the lungs of air breathing creatures.
Obviously fish exchange gasses in solution through their gills.
Most oil based paints contain hydrocarbons of some type.
Hydrocarbons are extremely toxic to living animals.
Hydrocarbons can and do exist in liquid and vapor phases, and in the gaseous phase - sure can enter the tankwater.
Any molecule in the air above the surface of the tankwater can move into solution. It depends on several things, it's own vapor pressure, the tankwater temperature, the ambient air temperature, atmospheric pressure, dewpoint/relative humidity and other factors as well.
Water molecules enter and exit the tank all the time, as a liquid moving to a vapor/gaseous state and back again. It's constantly phase shifting from one state to another.
Vapors and gasses in the room are doing the same thing. To what degree - I don't know - it all depends.
You place a 10 gallon marine tank in a phone booth with an open container of paint thinner ... close the door tight - that saltwater will contain traces of paint thinner ( hydrocarbons ) after a period of time.
Some people will cover the tank with clear plastic wrap like Saranwrap - then place an air pump "outdoors" with a long length of airline tubing running to a small hole in the plastic wrap, and allowing a few small pinholes in the sheet.
Keeping a *positive* pressure on the enclosed tank will keep most vapors/gasses from entering the tank.
The tank is fed with fresh air from outside the house.
Shutting down wet/drys, or other filtration for a period will reduce it as well - but you gotta be carefull when doing so.
This to me is the most sure fire of preventing tankwater/creatures exposure to airborne chemical compounds - such as paint or insectacide fumes.
It depends on the chemical - and it depends on the it's nature.